Automatic electrode integrity management systems and methods

ABSTRACT

This document discusses, among other things, systems and methods for automatic electrode integrity management. Interelectrode impedance is measured for various electrode combinations of an implantable cardiac function management device. The impedance data is processed, such as at an external remote server, to determine whether an electrode is failing or has failed, to select an alternate electrode configuration, to alert a physician or patient, to predict a time-to-failure such as by using population data, or to reprogram electrode configuration or other device parameters of the implantable cardiac function management device.

TECHNICAL FIELD

This patent document pertains generally to managing implantable medicaldevices and more particularly, but not by way of limitation, toautomatic lead integrity management systems and methods.

BACKGROUND

Implantable medical devices include cardiac function management devices,such as pacers, cardioverters, defibrillators, cardiac resynchronizationtherapy devices, or devices having a combination of such attributes.Such devices generally use electrodes, such as for sensing intrinsicelectrical heart signals, for delivering stimulations to induce heartcontractions, or for delivering a countershock (“shock”) to interrupt atachyarrhythmia. Such electrodes may include, for example: anintracardiac electrode located within a heart (e.g., on a multiconductoror other intravascular lead); an epicardial electrode located on theheart; or a can or header or other electrode located at or near anelectronics unit, which is generally implanted pectorally, abdominally,or elsewhere.

Mechanical stress may affect an intravascular intracardiac lead, havingmultiple such intracardiac electrodes located at or near its distal end,with multiple conductors leading to a connector at its proximal end,which connects to an implantable electronics unit of a cardiac functionmanagement system. Lead failures are a well established problem for themedical device industry. For example, an implantablecardioverter-defibrillator (ICD) lead failure rate of 2.73% at 56 months±28 months has been reported. See Dagrnara, et al., Occurrence of ICDLead Fracture Is Related to Foregoing ICD Replacement or LeadIntervention, Heart Rhythm, 2001. 1(1): p. S208-S209. Another examplereported a mean time to failure of 6.8±5 years for ventricular pacingleads and 6.0±4.2 years for atrial pacing leads. See Hauser et al.,Clinical Features and Management of Atrial and Ventricular Pacing LeadFailure: A Multicenter Registry Study, Heart Rhythm, 2004. 1(1): p. S13.Lead failures may take several different forms, or failure modes. Oneexample of ICD lead failures were classified as: 43% lead insulationfailures, 31% low voltage (e.g., pacing electrode) conductor failures,and 10% high voltage (e.g., shock electrode) conductor failures. SeeHauser et al., The Multicenter Registry's Experience with 4,059 ICD andPacemaker Pulse Generator and Lead Failures, Heart Rhythm, 2005, 2(5):p. S30. Lead failures can result in an apparent short circuit betweenelectrodes, or in an open circuit to one or more electrodes for sensingor delivering electrical energy. This can adversely affect performanceof the accompanying cardiac function management system. For example, fora tachyarrhythmia patient with an ICD, a lead failure may result in theICD inappropriately sensing mere noise as tachyarrhythmic cardiacdepolarizations, resulting in unwarranted delivery of a shock. Asanother example, for a bradycardia patient with a pacer, a lead failuremay result in loss of pacing, resulting in inadequate cardiac output forthe patient. In sum, lead failures can have serious consequences forpatients with cardiac function management devices.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 is a schematic drawing illustrating generally one example of animplantable cardiac function management device that is coupled to aheart using one or more intravascular leads.

FIG. 2 is a schematic drawing illustrating generally an example of adistributed patient management system for managing multiple implantabledevices, which are generally, but not necessarily, located in differentpatients.

FIG. 3 is a flow chart illustrating generally an example of using aserver for managing the electrode configuration of various implantablecardiac function management devices, such as for ensuring the integrityand proper functioning of such electrodes by monitoring electrodeimpedance.

FIG. 4 is a graph of impedance vs. time illustrating generally oneconceptualization of how population (or simulation or other predictive)information can be used.

FIG. 5 is a flow chart illustrating examples of various responses todetermining that a particular interelectrode impedance measurement isabnormal, such as by comparison to population data, or otherwise.

FIG. 6 is a flow chart illustrating an example that is similar to FIGS.3 and 5, but in which certain functions are performed within theimplantable device.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, logical and electrical changes may be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one. In this document, the term“or” is used to refer to a nonexclusive or, unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

FIG. 1 is a schematic drawing illustrating generally one example of animplantable cardiac function management device 100 that is coupled to aheart 102 using one or more intravascular leads 104. In thisillustrative example, a lead 104A has its proximal end connected to aheader 106 portion of the device 100, with the header 106, in turn,connected to a hermetically sealed electronics unit 108. In thisillustrative example, the distal portion of multi-conductor lead 104Aextends into a right ventricle of the heart 102, and includes a tipelectrode 110, a ring electrode 112, a distal shock electrode 114 and aproximal shock electrode 116. This example also shows a lead 104B thathas its proximal end connected to the header 106. The distal portion ofthe lead 104B extends into a coronary sinus or great cardiac vein, andprovides four electrodes 118A-D located near the left ventricle of theheart 102. Other leads may extend elsewhere, such as lead 104C extendinginto the right atrium, for example, to provide a distal tip electrode124 and a slightly more proximal ring electrode 126. The electronicsunit 108 of the device 100 may also include electrodes, such as a canelectrode 120 or a header electrode 122, or one or more other electrodeslocated at the device 100 or nearby, or one or more epicardialelectrodes, or any other suitable configuration of electrodes. Suchelectrodes may be individually connected back to the device 100 or, incertain circumstances, may share one or more common conductors back tothe device 100.

FIG. 2 is a schematic drawing illustrating generally an example of adistributed patient management system 200 for managing multipleimplantable devices 100A-N, which are generally, but not necessarily,located in different patients 202A-N. Each implantable device 100communicates with a server 204, which can be remote from one or all ofthe patients 202. The example of FIG. 2 shows intermediary transceivers206A-N for each of the implantable devices 202A-N, however, this is notnecessary. For example, the transceiver 206A communicates wirelesslywith the implanted device 100A, such as by a radio frequency (RF) link,an inductive link, or otherwise. The transceiver 206A also provideswired or RF or other wireless communication with the server 204, such asthrough a telecommunications or computer network 208. In this example,the patient management system 200 includes one or more computer or otheruser interfaces 210A-N, which communicate with the server 204 over thenetwork 208, such as via a wired or wireless link. Such a user interface210 permits a physician or other user to connect to the server 204, suchas for interacting with one or more of the implantable cardiac functionmanagement devices 100A-N. This may include reviewing or usingphysiological data or device settings communicated from an implantablecardiac function management device 100 to the server 204, or even forremotely programming an implantable cardiac rhythm management device100. The server 204 generally includes a processor 212 and data storage214 to help the user analyze cardiac function management device status,settings, and physiological data.

FIG. 3 is a flow chart illustrating generally an example of using theserver 204 for managing the electrode configuration of variousimplantable cardiac function management devices 100A-N, such as forensuring the integrity and proper functioning of such electrodes bymonitoring electrode impedance. Although FIG. 3 focuses on theinteraction between the server 204 and a particular cardiac functionmanagement device 100A, the server 204 will generally interact withmultiple such cardiac function management devices 100A-N, which aregenerally respectively implanted in different patients, although asingle patient could have multiple devices 100.

In the example of FIG. 3, at 300, an implantable cardiac functionmanagement device 100A tests interelectrode impedance for variousspecified combinations of two or more electrodes. An exemplaryillustrative list specifying combinations of electrodes for whichimpedance is to be tested is given in Table 1, which is provided by wayof example only, and not by way of limitation.

TABLE 1 Example of electrode combinations for testing impedance betweenfirst electrode(s) and second electrode(s) First Electrode(s) SecondElectrode(s) RV tip electrode 110 RV ring electrode 112 RA tip electrode124 RA ring electrode 126 LV electrode 118A LV electrode 118B RV shockelectrode 114 SV shock electrode 116 RV tip electrode 110 Can electrode120 RA tip electrode 124 Can electrode 120 LV electrode 118A Canelectrode 120 RV shock electrode 114 Can electrode 120 RV ring electrode112 Can electrode 120 RA ring electrode 126 Can electrode 120 LVelectrode 118B Can electrode 120 SV shock 116 Can electrode 120 Etc.Etc.In certain examples, the impedance will be tested between combinationsof multiple electrodes, such as between (1) electrodes 118A and 118B (incommon with each other) and (2) electrodes 118C and 118D (in combinationwith each other). Moreover, certain electrodes may appear in more thanone combination. For example, an electrode that appears in a failed orfailing electrode combination may nonetheless also appear in one or moreof the backup electrode combinations being tested, and may appear eitheralone, or in combination with one or more other electrodes.

In certain examples, an indication of interelectrode impedance ismeasured by delivering a specified fixed amplitude (e.g., typicallybiphasic) test current pulse between one or more commonly connectedfirst electrodes and one or more commonly connected second electrodes,and measuring the resulting voltage between the first and secondelectrode(s). The impedance is given by the measured voltage divided bythe specified current, and the actual impedance need not be calculatedsince the resulting voltage gives a signal that is proportional to, andtherefore indicative of, the interelectrode impedance. The deliveredtest current is optionally subthreshold in amplitude and frequency(e.g., 80 microamperes, 78 microsecond per phase of a four-phasebiphasic pulse train), such that it does not evoke a resulting heartcontraction. The test current can be generated, in certain examples,using a circuit that is also used for performing thoracic impedancemeasurements, such as for performing minute ventilation (MV) regulationof pacing rate. In other examples, the impedance measurement is madeusing, as a test energy or excitation energy, the energy deliveredduring a pacing pulse. In certain examples, the test current can bedelivered at a single electrode, and received by multiple electrodes. Incertain other examples, the test current can be delivered at multipleelectrodes and received by multiple other electrodes. In certain furtherexamples, the test current can be delivered at multiple electrodes andreceived by a single electrode. A list of candidate electrodecombinations to be tested is typically used to operate a multiplexer inthe electronics unit 108 to connect to the desired electrodes forperforming the desired impedance measurements. The interelectrodeimpedance testing at 300 is typically performed recurrently, such asperiodically with a specified frequency.

At 302, after the interelectrode impedance data has been collected forall the electrode combinations specified on a list, such as the listshown in Table 1, or a pre-specified subset thereof, then the resultingimpedance data is uploaded to the server 204 and stored in the datastorage 214, such as in a record associated with the particularimplantable cardiac function management device 100A from which it wasobtained. The uploading at 302 is typically performed recurrently, suchas periodically with a specified frequency, which may be different fromthe frequency of testing interelectrode impedance at 300. Thus, at 302,the data uploaded may include interelectrode impedance test dataacquired over a period of time between uploading events. In certainexamples, the uploading at 302 is initiated by the server 204, which“polls” the implantable cardiac function management devices 100. Inother examples, the uploading at 302 is initiated by the particularimplantable cardiac function management device 100, which “pushes” dataout to the server 204.

At 304, the interelectrode impedance data is compared to a history ofsuch data previously obtained from the same implantable cardiac functionmanagement device 100. This generally involves comparing data from eachtested electrode configuration to previously obtained data for the sameelectrode configuration, such as to determine whether there has been astatistically significant change. This may involve comparing the mostrecent data (or a short term average or the like) to earlier or longerterm data (such as an initial measurement, a long term average, or thelike).

At 306, if such a change in interelectrode impedance has been detected,then at 308 the changed interelectrode impedance data is optionallycompared to patient or population data. Patient data includes other datapreviously obtained from the same patient. Such a comparison helpsdetermine whether the observed change in interelectrode impedance in aparticular patient is significant with respect to previously observedmeasurement or trend data such that it represents an actual or impendingfailure. If no patient data is yet available (e.g., for a newlyimplanted lead), then predictive laboratory or simulation modeled dataor other data can be used for performing this comparison. Populationdata generally includes interelectrode impedance data from a likeelectrode configuration used by other implantable cardiac functionmanagement devices, e.g., 100B-N, that use the same type (e.g., model)of lead. Such a comparison helps determine whether the observednot-insignificant change in interelectrode impedance in a particularpatient represents an actual or impending failure already being observedin other patients. If no population data is yet available (e.g., for anew lead model), then predictive laboratory or simulation modeled dataor other data can be used for performing this comparison.

In making the comparison at 308 to population data, it may be desirableto normalize the interelectrode impedance data, such as to initial orearlier data obtained from the same patient, such that it is a change ininterelectrode impedance for a particular patient that is being comparedto corresponding changes in interelectrode impedance for the sameelectrode configuration as observed in other patients in the population.In certain examples, it is a trend over time of such normalized valuesfrom a particular patient that is compared to one or more trends overtime of such normalized values from other patients in the population.

Since various patients in the population may have experienced differentlead failure modes, in certain examples, the population data is analyzedsuch that data from patients deemed to exhibit the same failure mode areused together, such as in a composite trend over time for thatparticular failure mode. Data from a particular patient can be comparedto multiple such composite trends to determine whether the patient isexhibiting the signs of a particular failure mode. The ability toseparately represent and test for different failure modes separately mayincrease the predictive capability of the present techniques. Sinceinterelectrode impedance data is generally obtained and uploaded for allpossible electrode configurations, a failed or failing electrode can bepositively identified by comparing interelectrode impedance data for thevarious electrode combinations, and may not even require testing allsuch electrode configurations in order to make such a positiveidentification.

At 310, if the comparison at 308 indicates an abnormal interelectrodeimpedance for a particular electrode configuration, and that particularelectrode configuration is being used by the implantable cardiacfunction management device 100A for sensing or delivering electricalenergy, then at 312 an alternative electrode configuration can beselected. In certain examples, the particular electrode configurationhaving an abnormal impedance reading has a list of backup electrodeconfigurations that can be substituted for sensing or deliveringelectrical energy. In certain examples, a particular backup electrodeconfiguration is selected by comparing interelectrode impedance data forsuch alternative backup electrode configurations, and selecting aparticular backup electrode configuration using the comparison. In otherexamples, the list of backup electrode configurations is ordered, forexample, by similarity of locations of the electrodes in the backupelectrode configuration to the locations of the electrode configurationfor which it is being substituted, and the impedance data is only usedto choose between backup electrode configurations that are similarlylocated.

At 314, after a failed or failing electrode configuration has beenidentified at 310, and the most suitable backup electrode configurationhas been selected at 312, then, at 314, the particular implantablecardiac function management device 100A is automatically reprogrammed tothe selected backup electrode configuration, and an alert notifying ofthe same is automatically generated and communicated to one or more ofthe patient, the patient's physician, the manufacturer of the cardiacfunction management device 100A, or the manufacturer of the lead beingused by the cardiac function management device 100A. After 314, a “NoChange” determination at 306, or a “Not Abnormal” determination at 310,process flow then returns to 300, after an optional delay 316.

FIG. 4 is a graph of impedance (e.g., axis 400) vs. time (e.g., axis402) illustrating generally one conceptualization of how population (orsimulation or other predictive) information can be used, such as at 308in FIG. 3, or otherwise. In the example of FIG. 4, population-basedimpedance data for a particular electrode combination of a particularlead model is aggregated into population impedance data 404. In thisconceptualization, lead impedance is initially stable over time, thenincreases to a plateau, and then abruptly increases beyond a failurethreshold 406. In comparing an individual patient to the populationdata, an individual patient's location on the population curve 404 canbe located. If such location indicates impending failure, acorresponding alert can be issued to the patient, caregiver,manufacturer, regulatory agency, or another. If such location indicatesthat the patient is an “outlier” on the population curve 404, acorresponding alert can be issued to the patient, caregiver,manufacturer, regulatory agency or another.

Moreover, as seen in the illustrative example of FIG. 4, a predictedtime-to-failure, t₂-t₁, can be computed. Such information can beprovided, for example, to a physician to help the physician schedule anappointment to replace the lead before the predicted failure time, ifdesired. Moreover, as additional data is acquired from various patients,the threshold 406 can be adjusted in response, either automatically, orupon intervention by a human failure analysis engineer.

Furthermore, a patient's predicted future change in electrode impedancecan be used to adjust one or more device parameters of the patient'scardiac rhythm management device, either automatically, or usingcaregiver control. For example, pacing energy can be automaticallyincreased, depolarization sensing sensitivity can be automaticallyincreased. Similarly, if caregiver control is to be used, arecommendation of device parameter setting changes can be automaticallyprovided to the caregiver to alert and perform triage for the caregiver.

FIG. 5 is a flow chart illustrating examples of various responses todetermining that a particular interelectrode impedance measurement isabnormal, such as by comparison to population data, previous patientdata, or otherwise. In this example, at 500, impedance is tested betweenspecified electrodes. At 502, such information is uploaded to the server204. At 504, the information is compared to one or more criteria, suchas to a simple impedance threshold value or band, or to population orpredicted (e.g., computer-simulated) impedance data, which may representone or more failure modes. If, at 506, the a particular interelectrodeimpedance is deemed abnormal, then at 508, a responsive act is carriedout, such as delivering an alert at 508A, predicting and communicating atime-to-failure at 508B, reprogramming or recommending a differentelectrode configuration at 508C, reprogramming or recommending one ormore other changed device parameters (e.g., increase pacing energy,increase depolarization detection gain, etc.) at 508D, or triggeringanother device feature (e.g., trigger an automatic pacing threshold testto ensure proper pacing energy is being delivered) at 508E. Process flowreturns to 500, after any desired delay 510.

FIG. 6 is a flow chart illustrating an example that is similar to FIGS.3 and 5, but in which certain functions are performed within theimplantable device 100, rather than in the remote server 204. In thisexample, at 600, the implantable device 100 tests impedance or othercharacteristics between specified combinations of electrodes, such asdiscussed above. At 602, resulting information is optionally uploaded tothe remote server 204, such as for storing the device history, byitself, or as part of population data, or both. At 604, the remoteserver 204 downloads impedance related information to the implantabledevice 100. This may include, for example, criteria against which themeasured impedance is to be compared to detect an actual or impendingfailure. It may include, for example, information by which to predict atime-to-failure. It may include, for example, information about whichresponsive action to take in the event of an actual or impending leadfailure. The information may be based on population-derived data, theparticular implantable device's own historical data, simulated orpredicted data, or the like.

At 606, the impedance or one or more other characteristics is comparedto one or more criteria, such as to determine whether there is an actualor impending lead failure. If a particular electrode configuration failssuch a test, then at 608 a failure response is initiated, such asissuing an alert, predicting a time to failure, reprogramming anelectrode configuration, recommending or reprogramming one or more otherdevice parameters (e.g., pacing energy), triggering another devicefunction (e.g., a pacing threshold test), or the like. Otherwise, afteran optional delay at 610, process flow returns to 600. Although FIG. 6illustrates a particular example of task division between theimplantable device 100 and the remote server 204, other allocations willalso be suitable. In general, the remote server 204 advantageouslypermits population-based data to be used for a particular device, sincethe remote server 204 will typically communicate with and obtaininformation from multiple implantable devices 100 in various patients.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. Many other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled. In the appended claims, the terms “including” and “in which”are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. For example,reciting first, second, third, fourth, fifth, and sixth electrodes in aclaim does not mean that there must be six electrodes.

The Abstract is provided to comply with 37 C.F.R. §1.72(b), whichrequires that it allow the reader to quickly ascertain the nature of thetechnical disclosure. It is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

1. A method comprising: selecting a first combination of at least two electrodes for sensing or delivering an electrical energy from or to a heart, respectively, the first combination including one or more commonly connected first electrodes and one or more commonly connected second electrodes that are unconnected to the first electrodes; determining a first impedance between the first electrodes and the second electrodes; comparing the first impedance to one or more criteria to determine whether the first combination is adequate for the sensing or delivering the electrical energy; if the first combination is determined to be inadequate, then selecting between at least second and third combinations of at least two electrodes to determine which is more suitable for the sensing or delivering the electrical energy, the second combination of at least two electrodes including one or more commonly connected third electrodes and one or more commonly connected fourth electrodes that are unconnected to the third electrodes, the third combination of at least two electrodes including one or more commonly connected fifth electrodes and one or more commonly connected sixth electrodes that are unconnected to the fifth electrodes, the selecting including: determining a second impedance between the third electrodes and the fourth electrodes of the selected second combination of at least two electrodes; determining a third impedance between the fifth electrodes and the sixth electrodes of the selected third combination of at least two electrodes; and using the second and third impedance for the selecting between the at least second and third combinations; and sensing or delivering electrical energy from or to the cardiac tissue using the selected one of the second and third combinations of electrodes.
 2. The method of claim 1, comprising: measuring at least one secondary characteristic, the secondary characteristic selected from at least one of a pacing threshold, a defibrillation threshold, a sensed depolarization amplitude, and a sensed signal-to-noise characteristic; determining, using the secondary characteristic in combination with the measured first, second, or third impedance, at least one of: (1) whether the first combination is adequate for the sensing or delivering the electrical energy; and (2) which of the second and third combinations of at least two electrodes is more suitable for the sensing or delivering the electrical energy.
 3. The method of claim 1, in which the comparing the first impedance to one or more criteria is performed at an implantable device.
 4. The method of claim 1, in which the comparing the first impedance to one or more criteria is performed at a remote server.
 5. The method of claim 1, in which at least two of the first electrodes, the second electrodes, the third electrodes, the fourth electrodes, the fifth electrodes, and the sixth electrodes include the same electrode.
 6. A method comprising: repeatedly measuring electrode impedances for combinations of two or more electrodes located in association with a heart; recording, in a memory of an implantable cardiac device, information associated with the measured electrode impedances; collecting, in an external data storage, the recorded information for two or more implantable cardiac devices; creating one or more electrode impedance relationships for at least one of the implantable cardiac devices using the external database; and sending information to an implantable cardiac device that is derived from at least one of the electrode impedance relationships.
 7. The method of claim 6, comprising: measuring at least one secondary characteristic, the secondary characteristic selected from at least one of a pacing threshold, a defibrillation threshold, a sensed depolarization amplitude, and a sensed signal-to-noise characteristic; determining, using the secondary characteristic in combination with the measured electrode impedances for the combinations of two or more electrodes associated with the heart, a suitability of at least one of the combinations of two or more electrodes for sensing electrical energy from or delivering electrical energy to the heart.
 8. The method of claim 7, comprising comparing, using the secondary characteristic in combination with the measured electrode impedances for the combinations of two or more electrodes associated with the heart, combinations of two or more electrodes to determine suitability for sensing electrical energy from or delivering electrical energy to the heart.
 9. The method of claim 6, in which the recording includes storing at least one measured electrode impedance and corresponding measurement time, and further comprising transmitting the recorded measured electrode impedance and corresponding measurement time to an external device, and in which the creating at least one electrode impedance relationship includes creating an impedance trend over time.
 10. The method of claim 6, in which the creating at least one electrode impedance relationship includes generating one or more statistical ensembles of electrode impedances for the combinations of two or more electrode.
 11. The method of claim 6, in which the creating at least one electrode impedance relationship includes determining a change in electrode impedance for at least one of the combinations of two or more electrodes.
 12. The method of claim 6, in which the creating at least one electrode impedance relationship includes determining a historical impedance-electrode relationship for at least one of the combinations of two or more electrodes.
 13. The method of claim 6, in which the creating at least one electrode impedance relationship includes estimating a future electrode impedance value for at least one of the combinations of two or more electrodes.
 14. The method of claim 6, in which the creating at least one electrode impedance relationship includes determining an order of electrode combinations for sensing or delivery an electrical energy.
 15. The method of claim 6, in which the creating at least one electrode impedance relationship includes determining a population estimate of electrode impedances for similar electrodes used in various patients in a patient population.
 16. The method of claim 15, comprising downloading information from the population estimate to the implantable cardiac device.
 17. The method of claim 16, comprising using the downloaded information at the implantable cardiac device to determine the existence of an actual or impending lead failure.
 18. The method of claim 16, comprising using the downloaded information at the implantable cardiac device to determine a response to an actual or impending lead failure.
 19. A system comprising: an implantable cardiac function management device, configured to be coupled to combinations of at least two electrodes for sensing electrical energy from or delivering electrical energy to a heart, the cardiac function management device comprising: an electrode impedance measurement circuit, for determining a first impedance between one or more commonly connected first electrodes and one or more commonly connected second electrodes; a memory, communicatively coupled to the electrode impedance measurement circuit, the memory configured to store impedance information; a processor, communicatively coupled to the memory, the processor configured to select between electrode configurations, and to substitute a backup electrode configuration for a failed or failing electrode configuration, the backup configuration selected from multiple candidate electrode configurations by using measured impedances of the candidate electrode configurations.
 20. The system of claim 19, in which the implantable device comprises at least one measurement circuit that is configured to measure at least one secondary characteristic, the secondary characteristic selected from at least one of a pacing threshold, a defibrillation threshold, a sensed depolarization amplitude, and a sensed signal-to-noise characteristic, and wherein the processor is configured to determine, using the secondary characteristic in combination with the measured impedances of the candidate electrode configurations, at least one of: (1) whether the first combination is adequate for the sensing or delivering the electrical energy; and (2) which of the second and third combinations of at least two electrodes is more suitable for the sensing or delivering the electrical energy.
 21. The system of claim 19, wherein the implantable cardiac function management device includes a communication circuit, coupled to the processor, the communication circuit configured for communication with a remote external server, and wherein the processor of the implantable cardiac function management device is configured to use population impedance information received from a remote server to determine at least one of: (1) whether an electrode combination being used by at least one of the devices is failing or failed, or (2) a suitable backup electrode combination selected from the candidate back up electrode combinations.
 22. The system of claim 19, wherein the implantable cardiac function management device includes a communication circuit, coupled to the processor, the communication circuit configured for communication with a remote external server to communicate information about the first impedance to the remote external server.
 23. A system comprising: an external remote server, configured to be communicatively coupled to a set of implantable cardiac function management devices for obtaining impedance measurements from electrode combinations of each of the set of devices, the server comprising: a data storage, the data storage comprising an individual data storage for the measured electrode impedances of each of the set of devices; and a processor, configured to use the impedance measurements to detect a failed or failing electrode combination being used by at least one of the devices, and configured to select a backup electrode combination for the failed or failing electrode combination using impedance measurements for candidate backup electrode combinations.
 24. The system of claim 23, in which the server comprises: a population data storage for measured or predicted population impedance information associated with the set of devices; and wherein the processor is configured to use the population impedance information to determine at least one of: (1) whether an electrode combination being used by at least one of the devices is failing or failed, or (2) a suitable backup electrode combination selected from the candidate back up electrode combinations.
 25. The system of claim 23, in which the server is communicatively coupled to receive secondary information from the set of devices, the secondary information selected from a pacing threshold, a defibrillation threshold, a sensed depolarization amplitude, and a sensed signal-to-noise characteristic, and wherein the data storage is configured to store the secondary information, and wherein the processor is configured to use the secondary information in combination with the impedance to determine at least one of: (1) whether an electrode combination being used by at least one of the devices is failing or failed, or (2) a suitable backup electrode combination selected from the candidate back up electrode combinations. 